The present invention concerns a process and an apparatus for three-dimensional surveying.
A certain number of processes which allow three-dimensional readings to be taken are already known.
The oldest one is that of geodesic surveying, which can achieve excellent precision, but which has a very slow data collection speed. Therefore it is only possible to acquire a limited number of points during a reasonable period of time, and as a result the process cannot be used for a complex scene.
On the other hand, in photogrammetry (taking photographic views of the same scene from two different angles), the time of data collection is short, but the subsequent treatment by stereo restitution is complicated and expensive. Furthermore, the precision of this process is often insufficient.
A process of three-dimensional surveying has been proposed, to eliminate the disadvantage of these two methods, in which a scene is scanned by emitting a laser beam in its direction, the image of the laser spot obtained in this way is formed on at least one element of an assembly of photosensitive elements, the direction of the laser spot relative to the said assembly is deduced from the position of the excited receptor element in the said assembly of elements, and the three spatial coordinates of each point of scanning are calculated by triangulation on the basis of the orientation of the beam emitted and the said direction of the spot. Such a process is described in the French Pat. No. 2 129 747.
This process always yields insufficient results, because the emission of a laser beam can only be oriented with a precision which is much inferior to that with which the direction of the spot for reception can be measured. The overall precision of the reading is therefore directly limited by the precision of orientation of the laser beam.
It has therefore been proposed, for example in the French Pat. No. 2 363 779, to use at least two photosensitive receptors as the triangulation base, each of them forming an image of the laser spot exposed by the beam emitted. This process therefore requires that each point surveyed be viewed simultaneously from the point of emission of the laser beam and that of at least two photoreceptors. This results in new difficulties, since in surveying complex scenes, where masking phenomena are frequently produced, at least one of the lines of vision is often obscured.